Date   : Sun, 12 Nov 2006 04:46:48 +0000
From   : splodge@... (Richard Gellman)
Subject: 5 1/4" disc on PC

David Harper wrote:
>> This is because the floppy controller in the modern PC cannot read the
>> low density disks.
>>     
See other thread current in hot debate :)
> I am not convinced it has anything to do with this (despite the other debate 
> that is going on at the moment).
>
> It sounds to me like a stepping-speed problem. A 5.25" drive cannot be brand 
> new :-) and it might be that the stepper motor that moves the head cannot 
> cope with the speed it is being asked to move by the more modern BIOS.
>   
If I remember correctly, the controller simply asks the head to step in 
a particular direction; the amount of step is set in the drive itself, 
primarily by the stepper motor. Some drives have jumpers (or links in 
BBC Micro parlance) and a very fine stepper that allow the head step to 
be adjusted for differing disk formats.

When I tried using my drive with a PC, I had to change a jumper somewhat 
ironically marked "MS" to get it to work.

> I do not know Omniflop well, and do not know whether this is an adjustment 
> that can be made within it. If it is, then it would be worth trying.
>
> You probably won't be able to adjust the stepping speed from the BIOS 
> settings in the CMOS - PCs are just not that flexible.
>   
Neither is the floppy interface. The connection is low level type, i.e. 
it doesn't take commands or return result codes, etc. It has simple 
control lines such as step, step direction, track 0 sense, index sense, 
etc. This is what leads me to believe head step is configured in the drive.

There is one thing that makes think this might not be true, and that is 
the FDrive setting on the Master 128 (or keyboard links on the model B). 
This adjusts a head step time, but I believe this only allows to 
configure the machine to wait a certain period after issuing a step 
before assuming its safe to being operation again. I may be wrong on 
that though.
>> If you can get hold of an older PC, possible one with an FDC that is a
>> plugin board then that will be able to cope.
>>     
>
> I would agree that you should try it on an older PC (and if it won't work on 
> an old one, then throw it!) But if it will work on an old one, then I 
> suspect it is a BIOS rather than an FDC problem.
>   
Put OmniFlop to use. Once the driver is installed it does improve the 
chances of reading a disk dramatically (in my limited experience). But 
you *may* still need to adjust the drive itself before it'll play nice 
with a PC controller (or at least the BIOS/OS trying to initialize it).

-- Richard